Field of the Invention
The present invention relates to a light emitting diode, and more particularly, a light emitting diode that can realize different light spectrums and color temperatures by forming a plurality of light emitting portions within a single package.
Discussion of the Background
A light emitting diode is an electroluminescence device having a structure in which an n-type semiconductor of which major carriers are electrons and a p-type semiconductor of which major carriers are holes are joined together, and emits predetermined light through recombination of these electrons and holes. A light emitting diode consumes less electric power and has a longer service life as compared with conventional light bulbs or fluorescent lamps. The electric power consumption of a light emitting diode is less than a few tenth to a few hundredth of those of conventional illumination devices, and the life span thereof is several to several ten times, thereby having reduced electric power consumption and excellent durability. Further light emitting diode can be installed in a small space and durable against vibration. A light emitting device using such a light emitting diode is used for display and back light, and a study is actively in progress so as to apply to illumination. A white light emitting diode as well as a light emitting diode with a single color such as red, blue and green is recently released. It is expected that a demand will increase rapidly as light emitting devices using a white light emitting diode are applied to products for a car and illumination.
The organism of humans has the circadian rhythm that means the physiological rhythm repeats in a 24 hours cycle. For example, the human hormone cortisol known as stress hormone as well as melatonin known as sleep hormone have a big influence of alertness and sleep. In the morning the cortisol level is increasing as a basis for the day's activities. The minimum of cortisol is at midnight. In comparison the melatonin level drops in the morning. So sleepiness is reduced. But when the day is ending and it becomes dark the melatonin level is increasing and the sleeping hormone is effective and the basis for a healthy sleep.
In general, light influences the physiological rhythm of humans, and more particularly, the sunlight plays an extremely important role in such an influence. The color temperature of the sunlight is higher than 6000K in the morning and getting decreased during the afternoon gradually. The color temperature indicates a physical figure with Kelvin (K) for a color of a light source. The higher the color temperature is, the more the part of blue is, and the lower the color temperature is, the more the part of yellow-red is dominating. Further, the increasing color temperature makes activity and concentration of the brain increased and the decreasing color temperature makes the sensitivity active and the mind comfortable.
Light provides various feelings according to wavelength or color temperatures and has a great influence on the physiological rhythm of humans. If the physiological rhythm does not adapt properly, many diseases such as digestive trouble and chronic fatigue can be caused. Accordingly, a study on illumination devices with consideration of the circadian rhythm is in progress.
In case of a light emitting device using a conventional light emitting diode, a variety of methods of making white light have been proposed. A common method of making white light is to combine a part of the first light emitted from a light emitting diode chip and the second light which of wavelength is changed by phosphor by applying phosphor around a light emitting diode chip. Phosphor substances for making white light can be garnet phosphors, thiogallate phosphors, sulfide phosphors, silicate phosphors, oxynitride phosphors and so forth. However, a light emitting device using such materials has a disadvantage in that a scope of color temperature is narrow, the color rendering index is very low, and the stability of these lamps is unsatisfactory. That is, there is a problem that it is difficult to manufacture a light emitting device providing various light spectrums or color temperatures.